Extraction process



March 7, 1939. s. TIJMSTRA ExTRAcT-ION PRooEss Filed May 14, 1955 UNITED STATE EXTRACTION PROCESS Sljbren Tljmstra, Berkeley, Calif., assignor to Shell Development Company, San Francisco, Calif., a corporation of Delaware Application May 14, 1935, SerialNo. 21,321

8 Claims.

This invention relates to an improved process for solvent extracting liquid mixtures, and more particularly comprises an improvement whereby a component of intermediate solubility `is removed from a three component mixture.

It is frequently desired to remove the intermediate component from a liquid mixture of three components which are progressively more soluble in selective solvents, and to retain the 10 least soluble and most soluble components. In

applying the known methods of solvent extraction to such a purpose, it has heretofore been necessary to remove the two soluble components, further extract the mixture of these two compo- 1| nents to separate them, and then recombine the desired components. This necessitates the us'e of two lseparation steps and is uneconomical.

It is an object of my invention to provide a process for withdrawing the intermediate component from a three component liquid mixture in an economical manner. It is a further object of my invention to provide an improved process of the type described in which only the component of intermediate solubility isremoved from the feed mixture in the main extraction column in substantial amounts and in which such lesser amounts of the extremely soluble component-as are withdrawn from the extraction zone are returned. toit, thereby obviating the final mixing :o of the least soluble component after its withdrawal from the extraction zone with the most soluble component. of my'invention to provide a process of the type described in which the desired components are 35 combined prior to thestep of separating them from the solvent, thereby making possible the elimination of one separation step. ,l

With the above and other objects in view my invention consists of the combination of steps 40 more fully described and illustrated in the following specication and drawing, and specifically pointed out in the appended claims, it being understcod that numerous changes within the scope of the claims will be apparent and may be 45 resorted to without departing from the spirit of my invention or' sacrificing any of its advantages.

Referring to the drawing, which shows a ow sheet of one embodiment of my invention, I is an 50 extraction apparatus, and 3 a washing apparatus.

These may be single towers, provided with contact means or multistage treaters comprising mixers and centrifugal separating means for effecting the countercurrent contacting of two u liquids or any other devices for the counter- It is a still further object i current treatment of the liquids. 5, l and 9 are y three separating apparatus, such as distillation or fractionating columns, interconnected with pipes, as shown on the drawing and hereinafter described, and equipped with necessary valves, yl5 pumps, heaters, heat exchangers and adiuncts not shown.

In accordance with one mode of operation, a liquid mixture containing three components, A,

B and C, respectively, of which A is the least l0 soluble and C the most soluble in a selective solvent S, is introduced into apparatus I through pipe I I and extracted with a solvent medium containing the solvent S introduced at I3. Under extraction conditions prevailing within the` apl5 paratus two phases are formed, one of which, the rafllnate phase, is withdrawn through a pipe I5, and the other, the extract phase, through a pipe I1. The latter is hereinafter referred to as the first extract phase, and contains B. B and C in substantial amounts, and is conducted to apparatus 3, where it is washed with a solvent L supplied from a storage tank I9 through a conduit 2|. Solvent L is selected to have physical and/or chemical properties which render it at least partially immiscible with the solvent S, in the presence of components B and C,. permit it to dissolve the component B, and permit its ready separation from S, A, B and C by suitable means, such as fractionation, absorption, precipitation, etc.

The solvent L ows countercurrently to the first extract phase and under extraction conditions prevailing within the apparatus a second railinate phase, consisting primarily of S and C (and a small amount of L)', and a second extract phase are formed. In this operation solvent L washes out substantial amounts of component B, because B has a lower aillnity for S than the component C. Solvent L will, however, at the 40 same timedissolve a certain smaller amount of component C. According to the preferred mode of operation I prevent the retention of appreciable quantities of C by the solvent L by employing a double countercurrent operation in apparatus 3. In accordance with this operation fresh solvent S is introduced from storage tank 23 through valve 25 and inlet 21, so as to ow countercurrently to the rising extract phase. The scrubbed second extract phase which now consists substantially only of L+S+B is withdrawn at 29 and conducted to the separator 1, which may be a simple distillation device which discharges L and S through conduit 3|, and component B through conduit 33. A portion of the extract B 55,

near the rafnate discharge point I5. 'I'his solvent medium is rich in the component -C and contacts the phaserich in A produced in apparatus I, and removes from it substantial amounts of the component B. Being already saturated with respect to C. this solvent medium will permit the component C to remain in the raffinate phase which is withdrawn at I5, and is li'or convenience hereinafter referred to as the ilrst small amounts of `S and of L (unless L is excluded from the solvent medium. as described below) which may be separated from the components A-i-C' in the separator 5. This separator can be a distillation apparatus, which discharges A-i-C through outlet 45, and S-i-L through conduit 41 to solvent storage tank 23.

Since the rst railnate contains but a small amount of L, and since it would be returned to the apparatus 3 with the solvent through conduit 21, this operation is quite feasible. It may, however. oi'ten be desirable to maintain the solvent in tank 23 in a substantially pure state. In this event the separator 5 may be a fractionator, and operated to discharge S through conduit 41 and L through conduit 49.

It is not always necessary that apparatus 3 be a double countercurrent apparatus, Thus,' if the component C is not very valuable. or if its nature is such that it will not be substantially soluble in L, the valve may .be closed and/or a single countercurrent apparatus substituted for double countercurrent apparatus 3. In this case valve 5I will be opened and the fresh solvent introduced through conduit 53 to inlet I3, together with the second ramnate phase from conduit 4I.

As a further modiilcation, I may treat all or a portion of the second railinate phase which ows through conduit 4I in separator 9 to remove L and/or S. According to the mode oi' operation, valve 55 is opened and second ramnate phase admitted to separator 9 through conduit 51. The valve 43 may be closed or adjusted to permit a portion oi' the rafdnate phase to by-pass the separator 9. If the separator is operated as a simple distillation device, L and S are conducted through conduit 59 to conduit 2|. If 9 is operated as a fractionator, L will be dischargedthrough conduit 59 and S through conduit 9|. which returns the latter to the storage 23. In either event component C is reintroduced to apparatus I through conduit 63 and inlet I3.

It should be noted that it is necessary to supply suillcient solve] S to the apparatus I to remove sufficient amounts of component B. Ii the separator 9 is operated to remove excessive amounts ofv S from the second ramnate it is necessaryv to satisfy this deilciency by partially opening valve 5I and/or valve 65, and/or operating the separator 9 to permit substantial amounts of `S to be discharged through outlet 63.

Fresh solvents S and yL may be introduced annua :2mm conduits n and u to replenish the mm. Numerous modincations may be made in my process without departing from the spirit and.

scope of my invention. Although I have shown a situation in which the rst ramnatephase is lighter than the ilrst extract phase. and in which the second extract phase is lighter than the second raffinate phase, it is obvious that my process is applicable to) situations in which these conditions do not obtain. The apparatus I and/or 3 may be provided with temperature control means for providing a temperature gradient, as is well known in the art, and may be provided with such other auxiliary aids as may be desirable. The apparatus I and/or 3 could further be operated according to a batch process. Although the extraction would not be as complete, the removal of the middle component would, nevertheless. be realized. ramnate phase. This phase will also contain My invention may be employed to treat any three component mixture. An example is the treatment oi a hydrocarbon mixture which contains parafiinic hydrocarbons, secondary olenes. and tertiary oletlnes, the secondary oletlnes having an intermediate solubility. To remove these secondary olenes a polar solvent may be used as the main solvent S. Examples of solvents oi' this type are liquid sulfur dioxide, furfural, nitrobenzene, chlorex, phenols, isoquinoline, etc. Mixtures of a solvent or with other solvents or with diluents may also be employed.. A nonpolar solvent or a solvent of such` polarity as to be capable of forming two liquid phases when mixed with the extract phase may be used as the secondary solvent L. Saturated paramnic hy drocarbons, such as propane, or butane, or pentane, are examples of suitable secondary solvents. The solvent L should be selected so as to be easily separated from the oietlnes by distillation.

By the term component" is designated any of the three portions of any liquid mixture which portions can be separated from each other by extraction with a solvent or solvent mixture. Ii:A

In the present specication and claims, there is no diil'erenoe in meaning between thewords solution, "liquid mixture" and liquid solution.

I claim as my invention:

l. In a process for removing an intermediate component from a liquid mixture comprising three components of diierent solubilities in a ilrst selective solvent, the steps of ilowing said mixture in an extraction zone countercurrently to concurrent streams of said selective solvent and of a component which is more soluble than the said intermediate component under extracting conditions to form a ilrst ramnate phase and a first extract `phase containing said intermediate and more soluble components. separating said phases, subjecting said nrst extract phase in a washing zone to double countercurrent extraction with said tlrst selective solvent and a second solvent under conditions to form a second extract phase which is rich in said second vsolvent and in saidintermediate component and a second raiiinate phase which is rich in the more soluble components and in said ilrst selective solvent, and introducingvat least a portion oil said second should be present only in another component..

' the component of high solubility from the raframnate into vthe extraction sone to form the streams of selective solvent and oi the more soluble component, 'whereby lthe rst rafiinate phase is enriched by the' components of high solubility.

- a 2. 'I'he process according to claim 1 in which a portion of the secondv raffinate phase is treated to reduce its solvent content before it' is introduced into the extraction zone. y

3. The process for treating a liquid mixture comprising three -components of progressively diierent solubilities in'a selective solvent to remove a component oiintermediate solubility and produce a railinate phase concentrated inthe other components, which'comprises the steps of extracting said mixture in an extraction zone with said solvent by flowing said mixture and solvent countercurrently to each other to form a raihnate phase and an extract phase, the lattercontaining said intermediate component` and a more soluble component, separating the extract phase into portions, one oi' which is rich in the component of intermediate solubility and the other one of which is rich in the component of greater solubility, and enriching said raillnate by the component of high solubility by re-introducing the latter of said portions into the countercurrent extraction zone at a point so as to avoid countercurrent flow with respect to said solvent, whereby the washing out of said component oi high solubility from the rainnate is suppressed.

4. The process according tocla'im 3 in which Vthe treatment of the extract phase comprises the step o! removing the intermediate, component from the extract phase by washing it with a second solvent. f

5. The process for removing an intermediate component from a liquid mixturejcomprising three. components of progressively different solu bilities in a selective solvent, comprising the stepsv of ilowing said mixture in an extraction zone countercurrently to concurrent streams o! said selective solvent and of at least one component of greater solubilitythan said intermediate com-A ponent under extracting conditions to form rst extract and raiiinate phases, separating said phases, washing said first extract phase with a diiierentvsolvent to i'orm a second extract phase 'which is rich in the intermediate component, and

a second raiiinate phase-which is poorin the intermediate component.A and enriching said rst ramnate by said component of high solubility by introducing at least a portion oiisaid second ratiinate phase into said extraction zone together v with said solvent to form the stream of the more soluble component, whereby ythe washing out oi' nate is suppressed.

6. The process for removing an intermediate component from a liquid mixture comprising three components of progressively different solubilities in a. selective solvent, comprising the steps of owing said mixture in an extraction zone countercurrently to concurrent streams of said selective solvent and of. at least one component -of greater solubility than said intermediate component under extracting conditions to form rst extract and raffinate phases, separating said phases, washing said first extract phase with a diierent solvent to form a second extract phase which is rich in the intermediate component, and

a second rafnate phase which is poor in the intermediate component, treating said second extract phase to produce substantially pure extract of said substantially pure extract into the extraction zone as a backwash, and enriching said first raiiinate by said component of high solubility by introducing at least a portion of said second rafnate phase into said extraction zone together with said solvent to form the stream of the more soluble component, whereby the washing out of the component of high solubility from the rafiinate is suppressed.

7. A process for producing a mixture of parafiinic hydrocarbons and tertiary olefines comprising the steps of extracting a mixture of parafdnic hydrocarbons, secondary olenes, and tertiary olenes byI owing-said mixture countercurrently to a polar selective solvent in an extraction zone to produce a raiiinate phase and an extract phase, the latter containing both secondary and tertiary oleiines, but substantially no parafilnic hydrocartraction zone near the point ofwithdrawal of said raffinate phase from the extraction zone, located to avoid countercurrent ilow of said introduced phase with respect to the polar selective solvent,

whereby the washing out of tertiary oleilnes from the rafiinate is suppressed.

' of vintermediate solubility, introducing a portion 8. 'I'he process according to claim 3 in which the liquid mixture'comprising three components is a hydrocarbon mixture.

i SIJBRENTIJMSTRA. 

